The present invention generally relates to injectable liquid forms or microdispersions of polymers suitable for use in soft tissue repair, augmentation, and as viscosupplements.
A variety of different materials have been used to repair or augment soft tissue defects or to contour abnormalities caused by facial defects, acne, surgical scarring, trauma or aging. Unfortunately, none of these materials is considered to be ideal owing to short-comings in effectiveness or efficacy. For example, liquid silicone was often used to correct soft tissue defects. However, this material was subsequently banned by the FDA when it was discovered that it could migrate to distant parts of the body and cause physiological and clinical problems. Another material, bovine collagen, became available in the 1970's and appeared to be an effective material for treating soft tissue defects. Over time, however, it was discovered that this material was fairly rapidly absorbed. The rapid resorption was partially solved by crosslinking the collagen to extend its lifetime to six months; however, frequent injections of the material are still required. Furthermore, allergic reactions due to bovine proteins present in the collagen persist in the cross-linked material.
A number of newer materials for soft tissue or augmentation have been described. Ceramic particles of calcium phosphate mixed with an aqueous gel carrier in a viscous polymer have been described in U.S. Pat. No. 5,204,382 to Wallace et al. However, there appear to be risks associated with the use of these nonabsorbable particulate materials relating to their migration in vivo. Polymers in combination with solvents and a thermosetting material with a curing agent have both been proposed by Dunn in U.S. Pat. Nos. 4,938,763; 5,278,201; and 5,278,202, but the solvents necessary to dissolve the polymers appear to be less than acceptable, and the materials have limited utility in filling soft tissue defects because they solidify. Furthermore, these materials and other similar commercial materials have ultimate yield stresses close to 10,000 psi compared to between 500 and 2,000 psi for human skin, raising pulpability concerns and making them too hard for repair of soft tissue and especially for dermal augmentation or repair. Other polymer blends based on lactic acid polymers also have been suggested in U.S. Pat. No. 4,235,312 to Buchholz.
Other materials for injection, which solidify to serve as bulking agents or as matrices for tissue ingrowth, are described in U.S. Pat. No. 5,709,854 to Vacanti, et al., and PCT/US96/09065 by Reprogenesis. Exemplary materials in the '854 patent include alginate solutions which are mixed with calcium ions to induce crosslinking after injection. The PCT application discloses alternative crosslinkable synthetic polymers which have similar properties upon exposure to light or multivalent ions.
In this case, however, the polymers are considered to be too viscous to be injected through a needle, which significantly limits their utility. Furthermore, the oligomers also may be slightly soluble in body fluids, facilitating a rapid diffusion out of the site of implantation. To address these concerns, U.S. Pat. Nos. 5,728,752 and 5,824,333 to Scopelianos et al., disclose polymers derived from ε-caprolactone, trimethylene carbonate, and/or ether lactones with glycolide, lactide and p-dioxanone units, for use in the repair of soft tissues and augmentation which have lower viscosities and do not harden after implantation. While these compositions appear to have such desirable properties, these materials are fairly rapidly degraded and therefore would need to be re-injected at frequent intervals. Moreover, some of these polymers break-down to monomers well known to cause undesirable inflammatory responses in vivo.
It is therefore an object of the present invention to provide polymeric materials for soft tissue repair and augmentation that are safe, injectable, long lasting, bioabsorbable, and biocompatible.
It is a further object of this invention to provide methods for preparing and using such materials.